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Additive effects of two substitutions in dihydropteroate synthase (DHPS) for the development of sulfonamide-resistant Neisseria meningitidis are discussed. A two-amino-acid insertion and a single-amino-acid substitution, together, give new resistance, the gene for which may have been introduced by natural transformation. It was found that a normal chromosomally encoded DHPS of N. meningitidis cannot be changed to one that is sulfonamide-resistant by inserting a serine and glycine, as is seen in clinical isolates. Likely the resistance gene in the isolates evolved in another bacterial species.

The genetic background of sulfonamide resistance in Neisseria meningitidis was analyzed by site-directed mutagenesis. Mutations in the cloned dhps meningococcal genes expressed in Escherichia coli affected the enzymatic characteristics of dihydropterate synthase and modulated the function of the enzyme. Furthermore, changes in the Phe and Leu residues of the enzyme by DHOS mutagenesis affected enzyme kinetics and resistance to sulfonamides.

A comparison of sulfonamide-resistant and sulfonamide-susceptible strains of Neisseria meningitidis indicates interspecies transfer is responsible for both types of resistant strains. Comparing the dihydropteroate synthase (dhps) gene's amino acid sequences for the MO035 and BT227 and 3976 with susceptible genes showed a higher than normal divergence in amino acid and nucleotide sequences. Drug susceptibility was significantly changed when conserved amino acids in dhps were changed to corresponding amino acids.

Study of different plasmids reveal that the integrons which confer antibiotic resistance to genes are situated on genetic elements. The genetic element carrying the integron is a transposon Tn5090 which has two genes tniA and tniB encoding transposition proteins. Transposon Tn5090 has insertion sequences identical to those of Tn7, Tn552 and Mu and the entire family of transposons have related retroelements.

Tn5086 isa 15.3-kilobase transposon which contains the trimethoprim resistance function as well as resistance genes against sulfonamide and mercuric ions. The trimethoprim resistance gene (dhfr) isolated from Tn5086 was shown to be different from other dhfr's and was denoted as type VII. Tn5086 and Tn21 were demonstrated to be closely related. The differences in the genetic structure and the protein products of the two transposons are discussed.

The nucleotide sequences of the dihydropteroate synthase (dhps) genes in sulfonamide-susceptible and sulfonamide-resistant strains of Neisseria meningitidis representing serogroups A, B and C were described. The results indicated horizontal gene transfer and homologous recombination, rather than mutational change of the dhps gene, as the means for the acquisition of sulfonamide resistance. Moreover, the results showed that Neisseria gonorrhoeae and N. lactamica, but not N. subflava and Branhamella catarrhalis, contain homologous dhps genes.

Abstract Background Horizontal gene transfer is an important source of genetic variation among Neisseria species and has contributed to the spread of resistance to penicillin and sulfonamide drugs in the pathogen Neisseria meningitidis. Sulfonamide resistance in Neisseria meningitidis is mediated by altered chromosomal folP genes. At least some folP alleles conferring resistance have been horizontally acquired from other species, presumably from commensal Neisseriae. In this work, the DNA sequence surrounding folP in commensal Neisseria species was determined and compared to corresponding regions in pathogenic Neisseriae, in order to elucidate the potential for inter-species DNA transfer within this region. Results The upstream region of folP displayed differences in gene order between species, including an insertion of a complete Correia element in Neisseria lactamica and an inversion of a larger genomic segment in Neisseria sicca, Neisseria subflava and Neisseria mucosa. The latter species also had DNA uptake signal sequences (DUS) in this region that were one base different from the DUS in pathogenic Neisseriae. Another interesting finding was evidence of a horizontal transfer event from Neisseria lactamica or Neisseria cinerea that introduced a novel folP allele to the meningococcal population. Conclusion Genetic recombination events immediately upstream of folP and horizontal transfer have resulted in sequence differences in the folP region between the Neisseria species. This variability could be a consequence of the selective pressure on this region exerted by the use of sulfonamide drugs.

Objective: Existing information has shown that infants who are prenatally exposed to P. falciparum are susceptible to subsequent malaria infections. However, the effect of prenatal exposure to P. falciparum on parasite density during clinical malaria episodes has not been fully elucidated. This study is a component of a prospective cohort study for which initial results have been published. This component was designed to determine the effect of prenatal exposure to P. falciparum on parasite density during clinical malaria episodes in the first 24 months of life. A total of 215 infants were involved and monitored for clinical malaria episodes defined by fever (≥ 37 °C) and parasitaemia. The geometric mean parasite counts between exposed and unexposed infants were compared using independent samples t test. The effect of in utero exposure to P. falciparum on parasite density was assessed using binary logistic regression. Results: The geometric mean parasite count per µl of blood during clinical malaria episodes in exposed infants was 24,889 (95% CI 18,286–31,490) while in unexposed infants it was 14,035 (95% CI 12,111–15,960), P < 0.05. Prenatal exposure to P. falciparum was associated with hyperparasitaemia during clinical malaria episodes (OR 7.04, 95% CI 2.31–21.74), while other factors were not significantly associated (P > 0.05). [ABSTRACT FROM AUTHOR]

The high prevalence of sickle cell disease (SCD) and trait in Sub-Saharan Africa coincides with the distribution of Plasmodiumfalciparum malaria. Due to prolonged heavy use of chloroquine (CQ) as an antimalarial, drug resistance has developed. Many countries including Tanzania abandoned the use of CQ for uncomplicated malaria, except its use as prophylaxis in patients with sickle cell disease. This study investigated the prevalence of malaria in SCD patients and mutations associated with CQ resistance. Children diagnosed with sickle cell disease attending both outpatient clinic and those admitted at Bugando Medical Centre in northwestern Tanzania were screened for malaria using thick blood smear. A dried blood spot on Whatman filter paper was also taken for polymerase chain reaction (PCR) and restriction fragment length polymorphism. Among 123 known patients with sickle cell disease, the prevalence of malaria by blood smear microscopy was 3.2% and by PCR was 13.8%. The prevalence of K76T mutation among the patients was 81.3%. The majority of the patients (72.4%) were using chloroquine prophylaxis. In conclusion, the prevalence of malaria parasitaemia among children with sickle cell disease attending BMC is low (3.2%) by microscopy but several children maintain sub patent infection detectable by PCR. The prevalence of chloroquine resistant P falciparum in these children was higher than that previously seen in normal population in Tanzania. We recommend special attention to be paid to patients with sickle cell disease while studying the dynamics of drug resistant parasites.